This proposal explores a new hypothesis that space constancy, the stability of the visual world despite eye movements, is achieved on two levels: a perceptual level where the world must appear to be stable, and a motor level where recalibration of visual space with non-visual systems takes place. The project will examine mechanisms at both levels, and will apply the results to the problem of eyestrain in CRT computer terminals. Space constancy sometimes breaks down under difficult perceptual circumstances or in neurological patients. Perceptual space constance depends on a signal from the brain's eye movement control centers to other brain areas responsible for visual perception. In addition to this signal, several other poorly understood mechanisms contribute to space constancy. The first experiment concerns visual capture, the contribution of a static structured visual field to perception of the position of the visual world. We will ask which properties of the visual image contribute to visual capture, opening the possibility of desining artificial environments to minimize disorientation. The contribution of a dynamic suppression of perception of the displacements taking place on the retina during eye movements will be measured at several points on the visual field, and the generality of the suppression effect in other modalities will be assessed. The role of the retinal movement itself in generating suppression will be measured. Motor space constance, as far as is known, depends only on the neural signal from the eye movement control centers signalling the occurrence of a movement. The second part of the study investigates the accuracy of this signal and its storage in the brain. The third part of the study applies these results to the problem of eyestrain in CRT terminals, based on preliminary observations that space constancy is abnormal on these raster-generated displays. The abnormalities will be measured, and then terminals will be modified in an attempt to ameliorate the problem.